An official website of the United States government
Carbon-based black pigments, a widely used class of pigments, are difficult to differentiate with the noninvasive techniques currently used in cultural heritage science. We use pump-probe microscopy, coupled with a support vector machine, to distinguish common carbon-based black pigments as pure pigments, as two-component black pigment mixtures, and as a mixture of a black and a colorful pigment. This work showcases the potential of pump-probe microscopy to spatially differentiate carbon-based black pigments, which would have interesting applications to works of art.
more »
« less
Non-destructive three-dimensional imaging of artificially degraded CdS paints by pump-probe microscopy
Abstract Cadmium sulfide (CdS) pigments have degraded in several well-known artworks, but the influence of pigment properties and environmental conditions on the degradation process have yet to be fully understood. Traditional non-destructive analysis techniques primarily focus on macroscopic degradation, whereas microscopic information is typically obtained with invasive techniques that require sample removal. Here, we demonstrate the use of pump-probe microscopy to nondestructively visualize the three-dimensional structure and degradation progress of CdS pigments in oil paints. CdS pigments, reproduced following historical synthesis methods, were reproduced as oil paints and artificially aged by exposure to high relative humidity and light. The degradation of CdS to CdSO4·xH2O was confirmed by both FTIR (Fourier-transform infrared) and XPS (x-ray photoelectron spectroscopy) experiments. During the degradation process, optical pump-probe microscopy was applied to track the degradation progress in single grains, and volumetric imaging revealed early CdS degradation of small particles and on the surface of large particles. This indicates that the particle dimension influences the extent and evolution of degradation of historical CdS. In addition, the pump-probe signal decrease in degraded CdS is observable before visible changes to the eye, demonstrating that pump-probe microscopy is a promising tool to detect early-stage degradation in artworks.
more »
« less
- Award ID(s):
- 2108623
- PAR ID:
- 10502685
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Journal of Physics: Photonics
- Volume:
- 6
- Issue:
- 2
- ISSN:
- 2515-7647
- Format(s):
- Medium: X Size: Article No. 025013
- Size(s):
- Article No. 025013
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Titanium dioxide (TiO2) has been used in numerous paintings since its creation in the early 1920s. However, due to this relatively recent adoption by the art world, we have limited knowledge about the nature and risk of degradation in museum environments. This study expands on the existing understanding of TiO2facilitated degradation of linseed oil, by examining the effect of visible light and crystallographic phase (either anatase or rutile) on the reactivity of TiO2. The present approach is based on a combination of experimental chemical characterization with computational calculation through Density Functional Theory (DFT) modeling of the TiO2-oil system. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FT-IR) enabled the identification of characteristic degradation products during UV and visible light aging of both rutile and anatase based paints in comparison to BaSO4and linseed oil controls. In addition, cratering and cracking of the paint surface in TiO2based paints, aged under visible and UV–vis illumination, were observed through Scanning Electron Microscopy (SEM). Finally, Density Functional Theory (DFT) modeling of interactions between anatase TiO2and oleic acid, a fatty acid component of linseed oil, to form a charge transfer complex explains one possible mechanism for the visible light activity observed in artificial aging. Visible light excitation of this complex sensitizes TiO2by injecting an electron into the conduction band of TiO2to generate reactive oxygen species and subsequent degradation of the oil binder by various mechanisms (e.g., formation of an oleic acid cation radical and other oxidation products). Graphical Abstractmore » « less
-
Lim, Teik-Thye; Vilar, Vítor (Ed.)The detection and removal of Atrazine (ATZN), a pesticide of environmental concern, requires more efficient methods to facilitate its degradation. The adequate structural morphology, high specific surface area, great photothermal conversion performance, higher amount of oxygenated functional groups, and intense and stable fluorescence signals are considered as favorable properties of the materials used in the in the proposal of physicochemical methods for detection, capture and degradation of nitrogenous herbicides. Herein, the design, preparation, and characterization of MnFe2O4@CDs as a dual-functional material is reported. Due to its optical, photothermal, textural and surface chemistry properties, the material is able to capture, detect, and degrade the herbicide "Atrazine" in synthetic samples. The preparation of the proposed composites, formed by particles of bimetallic oxides (Mn-Fe2O4) and a covering of carbon dots (CDs), was confirmed using various characterization techniques including SEM, TEMHR, RAMAN, FTIR, UV-Visible, Photoluminescence, DRX, N2 adsorption-desorption isotherms, superficial chemistry, and photothermal. The study revealed that the ATZN capture occurs through hydrogen bonding interaction between −COOH and −COH functional groups exposed on CDs surface and amine groups −NH− of the herbicide. Furthermore, the CDs behave as fluorescent markers of single-channel employed to detect ATZN and to monitor the capture-degradation process. The MnFe2O4@CDs composite was integrated as the main thermoactive material into a photothermal reactor on which was incident a NIR laser. The high near-infrared absorption of the Mn-Fe2O4 particles resulting in an efficient photothermal conversion; which in turn, increase the temperature of the surrounding medium. The increase in temperature promotes the activation of persulfate (PS) at the interface of the MnFe2O4@CDs−PS system producing SO4• − radicals as oxidizing agents of atrazine. Our results demonstrate that the process may effectively degrade 99 % of atrazine for a concentration of CATZN [20 mM], when NIR light irradiated by 45 min and the system reaches a temperature of ca. 53 ºC. Additionally, the degradation of ATZN was confirmed by analysis of total organic carbon (TOC). The fluorometric analytical assay by CDs-base fluorescence probes allowed following the FL signal at 520 nm(λexit = 375 nm) for the capture “turn on” and degradation “turn off” of atrazine. Finally, as a comparison, we highlight the significant efficiency shown by the process studied here, compared to other similar atrazine degradation processes previously reported.more » « less
-
Photocatalysis, mainly using TiO2 as a catalyst, has emerged as a promising method to address the issue of wastewater treatment. This study explores the enhanced photocatalytic activity of TiO2 through the introduction of reduced graphene oxide (rGO) and cadmium sulfide (CdS) as selective metal dopants. The incorporation of rGO and CdS into the TiO2 lattice aims to optimize its photocatalytic properties, including bandgap engineering, charge carrier separation, and surface reactivity. The unique combination of CdS and rGO with TiO2 is expected to boost degradation efficiency and reduce the reliance on expensive and potentially harmful sensitizers. This experimental investigation involves the synthesis and characterization of TiO2-based photocatalysts. The photocatalytic degradation of methyl orange (MO) and methylene blue (MB) was assessed under controlled laboratory conditions, studying the influence of metal dopants on degradation kinetics and degradation efficiency. Furthermore, the synthesized photocatalyst is characterized by advanced techniques, including BET, SEM, TEM, XRD, and XPS analyses. The degraded samples were analyzed by UV-Vis spectroscopy. Insights into the photoexcitation and charge transfer processes shed light on the role of metal dopants in enhancing photocatalytic performance. The results demonstrate the potential of a TiO2-rGO-CdS-based photocatalyst in which 100% degradation was achieved within four hours for MO and six hours for MB, confirming efficient azo dye degradation. The findings contribute to understanding the fundamental principles underlying the photocatalytic process and provide valuable guidance for designing and optimizing advanced photocatalytic systems. Ultimately, this research contributes to the development of sustainable and effective technologies for removing azo dyes from various wastewaters, promoting environmental preservation and human well-being.more » « less
-
Abstract With the rapid growth of the lithium‐ion battery (LIBs) market, recycling and re‐use of end‐of‐life LIBs to reclaim lithium (Li) and transition metal (TM) resources (e.g., Co, Ni), as well as eliminating pollution from disposal of waste batteries, has become an urgent task. Here, for the first time the ambient‐pressure relithiation of degraded LiNi0.5Co0.2Mn0.3O2(NCM523) cathodes via eutectic Li+molten‐salt solutions is successfully demonstrated. Combining such a low‐temperature relithiation process with a well‐designed thermal annealing step, NCM523 cathode particles with significant Li loss (≈40%) and capacity degradation (≈50%) can be successfully regenerated to achieve their original composition and crystal structures, leading to effective recovery of their capacity, cycling stability, and rate capability to the levels of the pristine materials. Advanced characterization tools including atomic resolution electron microscopy imaging and electron energy loss spectroscopy are combined to demonstrate that NCM523's original layered crystal structure is recovered. For the first time, it is shown that layer‐to‐rock salt phase change on the surfaces and subsurfaces of the cathode materials can be reversed if lithium can be incorporated back to the material. The result suggests the great promise of using eutectic Li+molten–salt solutions for ambient‐pressure relithiation to recycle and remanufacture degraded LIB cathode materials.more » « less
